The present invention relates to a method for operating a sheet-fed offset press and, more particularly, to a method for operating a sheet-fed offset press in which an oscillating roller accomplishes an oscillating motion. Also, the present invention relates to an oscillation mechanism for an oscillating roller in an ink supply system for a sheet-fed offset press.
First, a method for operating a sheet-fed offset press, which relates to the present invention, will be described.
To distribute ink on rollers, some number of ink rollers in an offset press have so far been oscillated in the axial direction of the rollers. For a multi-color sheet-fed offset press in which ink rollers are oscillated, sheets supplied from a sheet-feeder are generally printed in one color at each printing station. Each printing station consists of an ink supply system, a dampening system for supplying water, and a number of rollers. Some of these rollers act as oscillating rollers that serve to distribute ink in the roller-width direction.
Many of these oscillating rollers always oscillate by a fixed amount. However, if the oscillating motion of the oscillating rollers continues during the time when printing operation is stopped temporarily for some reason, an ink supply-demand balance between ink transferred to a sheet and ink on the roller, which has been attained during printing operation, is lost undesirably. Specifically, during a steady printing operation, a balance is maintained between the amount of ink supply and the amount of ink transferred to paper sheets such that in printing portions where ink transfers to sheets, the ink supply amount increases, and in non-printing portions where only a small amount of ink transfers to the sheet, the ink supply amount decreases. Therefore, the ink distribution in the axial direction on the rollers is not uniform. However, when the press operation is stopped for some reason, for example, for an error in sheet position setting, if the oscillating rollers continue to be driven, the distribution of ink on the rollers becomes uniform by the distributing effect of the oscillating motion. As a result, when the printing operation is restarted, a number of paper sheets are printed with undesirable nonuniformity until the balanced state maintained before the stoppage of printing operation is achieved again.
In recent years, in some offset presses, the oscillation is started and stopped according to the timing of press operation to decrease such spoilage at the start of printing operation. An example of such a press is in Japanese Patent Laid-open Publication No. 11-240139 (No. 240139/1999). In this press, as the printing operation is started, the oscillation of the oscillating roller having a null or minimum amplitude at first is gradually increased, and the amplitude of the oscillating roller reaches a maximum when a form roller is brought into contact with a plate cylinder. In addition, Japanese Patent Publication No. 7-102698 (No. 102698/1995) discloses a printing press in which the oscillation is started or stopped at the same time that a form roller is separated from or is brought into contact with a plate cylinder.
Next, a conventional oscillation mechanism for an oscillating roller in an ink supply system for a press will be described.
A conventional example of an oscillation mechanism for a form roller, which has been disclosed in the aforementioned Japanese Patent Provisional Publication No. 11-240139 (No. 240139/1999), is explained below with reference to FIG. 9 showing the outline of a general offset press, FIG. 10 showing a oscillation drive system, FIG. 11 showing an essential part of a mechanism for starting and stopping oscillation, and FIG. 12 showing a cross section of FIG. 11.
Referring now to FIG. 9, paper sheets supplied from a sheet-feeder 301 are printed in a printing system 302, and are stacked and discharged to a sheet discharge section 305. The multi-color printing system 302 such as an offset press is composed of a plurality of printing units 302a, 302b, 302c and 302n provided according to the number of printing colors, and each printing unit include an ink supply system 303 for supplying ink, which is composed of a plurality of rollers, and a dampening system 304 for supplying dampening water. Of these systems, the ink supply system 303 is provided with a plurality of oscillating rollers 306 that oscillate in the axial direction to slidingly rub form rollers in order to distribute ink uniformly in the width direction.
FIG. 10 is a system diagram of a drive for oscillating the oscillating rollers 306. In this drive system, a driving force is transmitted from a crank of an oscillation drive source 307, which is driven by a drive system 309 for the machine, to an oscillation drive pin 310 provided at the tip end of an oscillation drive lever 311 via a drive link 308. Also as shown in FIG. 12, the oscillation drive lever 311 oscillates around a pin 312 provided on bearers 318 fixed to a machine frame. An oscillating lever 313, which oscillates around the pin 312 in the same way, consists of portions 313a and 313b for driving the oscillating rollers 306 and a portion 313c subjected to an oscillating force by the oscillation drive pin 310.
At the end of the oscillating lever 313a, 313b is provided an oscillation transmitting portion (details thereof is omitted) 317 for transmitting the oscillating force to the shaft end of the oscillating roller 306. Also, the portion 313c is provided with an oscillation drive changeover mechanism 319 that is composed of a change over member 314 engaging with the oscillation drive pin 310 to accomplish a changeover from transmission to stoppage of oscillation and vice versa and a changeover actuator 316 which moves the changeover member 314 to accomplish a changeover from transmission to stoppage of oscillation and vice versa.
As shown in FIG. 11, the changeover member 314 is formed with an arcuate elongated hole 315 such that there is a gap large enough for the oscillation drive pin 310 to slide, and the oscillation drive pin 310 is moved by the drive link 308 so that the range of oscillation produced by the oscillation drive lever 311 is not interfered. Thus, as shown in FIG. 12, the changeover member 314 engages with the oscillation lever 313c so as to fit to it and be capable of turning around the oscillation drive pin 310.
The changeover member 314 is moved by the actuator 316 or change over the direction of the elongated hole 315 from A to B and vice versa in FIG. 11, by which the oscillation force is transmitted and stopped. Specifically, when the changeover member 314 is made in the state of A by the actuator 316, the oscillation drive pin 310 oscillated by the oscillation drive lever 311 oscillates only in the elongated hole 315, so that the oscillation force is not transmitted to the oscillation lever 313. On the other hand, when the changeover member 314 is made in the state of B, the oscillation force can be transmitted.
In these related arts, the timing of start or stop of oscillation consists of synchronization with the contact of form rollers with the form plate and the start and stop of printing operation. According to a study made by the inventors, it has been found that the timing of start and stop of drive of oscillating rollers described in the related arts is not always optimum. Accordingly, an object of the present invention is to provide a method in which the drive of oscillating rollers is optimized, and spoilage caused by the short-time stoppage of a printing press during operation is minimized.
The present invention provides a method for operating a sheet-fed offset press in which an oscillating roller accomplishes an oscillating motion, comprising: a step of receiving a command to stop printing operation; a step of stopping the oscillating motion of the oscillating roller; and a step of separating a form roller from a form plate after a plate cylinder rotates 2 to 7 turns subsequently.
Also, the present invention provides a method for operating a sheet-fed offset press in which an oscillating roller accomplishes an oscillating motion, comprising: a step of receiving a command to start printing operation; a step of bringing a form roller into contact with a form plate placed on a plate cylinder; and a step of starting the oscillating motion of the oscillating roller after the plate cylinder rotates 2 to 7 turns subsequently.
The method in accordance with the present invention embraces various methods and is not subject to any special restriction if there is provided an oscillating roller such that the oscillating motion thereof can be turned on and off and the amplitude of the oscillating motion can be changed. Also, the drive system of the oscillating roller is not subject to any special restriction. For example, the mechanisms described in the aforementioned Japanese Patent Provisional Publication No. 11-240139 and Japanese Patent Publication No. 7-102698 and preferably a mechanism described below can be utilized to accomplish the oscillating motion of the oscillating roller.
As described above, according to the method in accordance with the present invention, the oscillating motion of the oscillating roller in the sheet-fed offset press can be controlled properly. Therefore, when printing operation is restarted after interruption, a proper ink film thickness profile can be formed rapidly, so that the occurrence of spoilage caused by nonuniform printing can be reduced.
On the other hand, as is apparent from the above description, for the conventional oscillation mechanism for the oscillating roller, the portions for transmitting an oscillating force from the oscillation drive pin 310 to the changeover member 314 are portions indicated by C1 and C2 of FIG. 11, which provides line-to-line contact. Therefore, wear takes place rapidly, and a gap caused by wear produces an impact force when a force is transmitted, which further accelerates wear. Therefore, parts must be replaced early due to wear and breakage.
Also, the changeover actuator 316 requires a large force because a difference between the distance L1 from the turning center of the changeover member 314 to the resistance portion and the distance L2 from the turning center of the changeover member 314 to the point of application for changeover is small. Therefore, the changeover actuator 316 having a high capacity is needed. Therefore, since the size of the changeover actuator 316 is made large, the size of the whole mechanism increases, so that the efficiency of utilization of tight space is decreased.
In view of the above situation, another object of the present invention is to provide an oscillation mechanism for an oscillating roller in which wear of a changeover member for transmitting and stopping an oscillating force is prevented to prolong the life, and the force for changeover is made low to enable a changeover actuator with a low capacity to be used, whereby space saving and low cost are provided, and failure and wear are reduced.
To achieve the above object, the present invention provides an oscillation mechanism for an oscillation roller in an ink supply system for a printing press, comprising an oscillating lever which oscillates around a support point with a predetermined angle to give an oscillating force to an oscillating roller and is formed with oscillation drive bearing portions on both sides on the opposite sides of the support point; first and second energizing members which are in contact with the oscillation drive bearing portions to give a pressing force; and a reciprocating drive means for transmitting a pressing turning force in the normal or reverse direction to the first and second energizing members by reciprocating motion, wherein the transmission of oscillation is stopped by the separation of the first energizing member from the oscillation drive bearing portion.
According to the above-described configuration, the mechanism for transmitting and stopping an oscillating force consists of the pressing of the energizing member to the oscillation drive bearing portion and the separation of the energizing member from the oscillation drive bearing portion, so that there is nothing that is worn. Therefore, wear and breakage caused by the line-to-line contact as in the case of the related arts can be prevented.
Oscillating force transmitting means is characterized in that the first energizing member is pivotally supported by a second support point coaxial with the reciprocating drive means, and the second energizing member is pivotally supported coaxially with the support point of the oscillating lever, whereby the energizing members are turned around the support point of the oscillating lever by an arm connecting the support point of the oscillating lever to the second support point.
According to the above-described configuration, a complicated construction such that the changeover member is fitted on the oscillation drive pin as in the case of the related arts is not needed, and a difference between the distance from the turning center to the resistance portion and the distance to the point of application for changeover can be increased. Therefore, changeover can be effected with a small force, so that an actuator with a low capacity can be used, whereby the mechanism can be configured at a low cost.
Also, another oscillating force transmitting means is characterized in that the energizing members are reciprocatively driven by an arm which pivotally supports the first energizing member at one end, pivotally supports the second energizing member at the other end on the opposite sides of the support point, and further pivotally supports reciprocating drive means at one end. By this configuration, the mechanism can be configured more simply.
Means for separating the first energizing member from the oscillation drive bearing portion is an actuator engaged with the first energizing member. By using such an actuator, the transmission and stoppage of an oscillating force can always be effected.
Also, the transmitting portion for transmitting an oscillating force to the oscillating roller is characterized in that the oscillation drive bearing portion and energizing member are brought into face-to-face contact with each other.
By the face-to-face contact between the oscillation drive bearing portion and the energizing member, wear etc. of the changeover member brought about in the conventional example is eliminated, so that the oscillation mechanism for the oscillating roller that is less failed and worn can be provided.